Supplementing lab analysis with inline measurements

Reduce production downtime, off-spec product, and time-consuming manual grab sampling in food plants with inline instrumentation.


Figure 1: Taking samples from the process for analysis in the plant’s lab is the tried-and-true method for ensuring quality control. It’s also expensive and not a real-time measurement. Courtesy: Endress+HauserFood plant managers are faced with many challenges today, not the least of which is ensuring product quality. Depending on the product being made, they may have to meet the requirements of the U.S. Food and Drug Administration (FDA), European Union (EU), and an alphabet soup of other agencies and regulations, including cGMP, GFSI, ISO, HACCP, SQF, SID, etc. These regulations specify proper ingredients, chemical and biological hazards, procedures, and sanitary conditions.

Food plant managers also have to meet the expectations of consumers for proper taste and texture. For example, the pH of certain products is critical, because it can affect taste as well as food safety. When adding citric acid to jams, beverages, and other products for acidification, pH must be carefully controlled.

On top of the obvious food safety and product quality challenges, a plant manager also needs to address operational issues and goals such as:

  • Product loss reductions
  • Variability in raw materials
  • Resource conservation, such as energy and water reductions
  • Loss of qualified operators and maintenance people
  • Need to reduce operating and maintenance budgets, and
  • Preparation and management of documentation for internal and external audits.

Currently, food plants typically rely on laboratory analysis (Fig. 1) of samples collected manually to ensure product quality at various points in a process. Lab technicians periodically take a grab sample, hurry back to the lab for a quick analysis, and communicate the result to the control room. Operators and maintenance personnel then make adjustments and corrections to improve control of the process, or to make repairs when required.

The challenge with relying on lab analysis is that it’s not done in real time, it’s time consuming, it’s labor intensive, and it has possibility for manual errors. If it takes 30 minutes to grab a sample and analyze it, then the result represents where the process was 30 minutes ago—not where it is now. The result could be a spoiled batch. If the measurement had been done inline, a sudden deviation would be detected instantly, allowing for an immediate corrective action that could save the batch.

Many types of inline analyzers are available and can be used for online quality control to supplement or replace laboratory testing, speed up measurements, enable immediate corrective actions, and automate the parts of a quality control system.

Inline analyzers

Inline analyzers are not available for every type of measurement in the food industry, but are available for many common measurements now being performed in labs.

Using inline analyzers helps manage many issues. For example, the amount of disinfectant used on a hydro cooker for canned food needs to be controlled closely to ensure food safety, as overdosing can cause corrosion and waste of chemicals, while too little can compromise food safety.

One plant previously monitored disinfectant by taking grab samples to a lab for analysis twice an hour. Inline analyzers were installed to measure free chlorine, pH, and conductivity of the disinfectant. Real-time measurement saved $13,000 annually in disinfectant costs by eliminating overdosing. These measurements allowed the automation system to add makeup water based on measured values, saving on heat energy and water usage, and producing less wastewater. The inline analyzers also eliminated the need to send a lab worker to the hydro cooker two times an hour to take grab samples. The bottom line was a payback period of just seven months.

In a similar example of how inline analyzers can cut expenses, a cheese plant performed five clean-in-place (CIP) operations per day. The chemicals cost $1,771 for a 30-gal drum, and the plant used three to four drums per month.

The plant installed an optical-phase separation sensor that used visible and near-infrared wavelengths of light to perform tests for product loss detection, interface detection, suspended solids, and turbidity measurements.

By measuring phase separation between whey, water, and CIP detergent in the line, operators were able to determine when the pre-rinse and CIP was complete, instead of relying on lab measurements and timing. Each CIP cycle was reduced by 15 minutes, and the plant cut CIP chemical consumption by 32%. The cost savings were $5,300 in the first three months on chemicals alone, plus savings from reduced energy and water use. The plant also increased equipment availability for processing by more than one hour per day.

Inline analyzers are nothing new, of course. Many of these measurements have been available for several years and are used for traditional process control applications. What’s new today is increased reliability, along with new features and capabilities:

Improved reliability: Experiences in the real world with traditional analyzers have been mixed. Trying to apply equipment designed for use in the lab directly in a process usually led to disappointments. Washdown, high temperatures, aggressive cleaning chemicals, and other environmental factors often resulted in equipment failures and maintenance nightmares. These problems have been rectified by designing analyzers and other inline instrumentation from the ground up for use on the plant floor and in the field.

Seamless integration: Traditionally, instruments were analog devices with a single 4-20 mA output. Today, the availability of digital outputs such as EtherNet/IP, Profibus, Foundation fieldbus, and HART is making integration of information into automation and information systems very easy, and also allowing multiple parameters to be obtained from a single device. For example, a Coriolis flowmeter can provide mass flow, volume flow, multiple totalizer values, density, viscosity, and temperature measurements along with diagnostic information over one set of wires (or wireless). These digital protocols also help improve accuracy by eliminating A/D conversions and loss of resolution during signal transmission in an analog 4-20 mA signal.

Simplified calibration: With expanding digital sensor technologies, the lab can now take responsibility for calibration of quality-related measurements. For example, to calibrate a pH sensor in the past, calibration equipment had to be brought into the plant. Today, this calibration can be done in the lab in a controlled environment, and the pre-calibrated sensors can be easily placed in operation. E+H’s Memosens and other similar technologies make this possible for pH, DO, conductivity, turbidity, chlorine, and many other parameters.

Hygienic design: One of the limiting factors for inline quality monitoring has been the lack of instruments meeting hygienic design requirements and resistant to thermal processing and CIP chemicals. Today, most instruments meet EHEDG or 3-A sanitary standards and are designed for use in the food industry. An example is pH measurement, which most people associate with glass sensors—a big problem in food processing as glass sensors can break and end up as foreign objects in the final product. Now there are reliable non-glass pH sensors that meet food processing requirements.

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